RETURNVALUE

On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.

ERRORS

EFAULTbuf is not valid.

CONFORMINGTO

POSIX.1-2001, POSIX.1-2008, SVr4. There is no uname() call in 4.3BSD.
The domainname member (the NIS or YP domain name) is a GNU extension.

NOTES

This is a system call, and the operating system presumably knows its
name, release and version. It also knows what hardware it runs on.
So, four of the fields of the struct are meaningful. On the other
hand, the field nodename is meaningless: it gives the name of the
present machine in some undefined network, but typically machines are
in more than one network and have several names. Moreover, the kernel
has no way of knowing about such things, so it has to be told what to
answer here. The same holds for the additional domainname field.
To this end, Linux uses the system calls sethostname(2) and
setdomainname(2). Note that there is no standard that says that the
hostname set by sethostname(2) is the same string as the nodename field
of the struct returned by uname() (indeed, some systems allow a
256-byte hostname and an 8-byte nodename), but this is true on Linux.
The same holds for setdomainname(2) and the domainname field.
The length of the fields in the struct varies. Some operating systems
or libraries use a hardcoded 9 or 33 or 65 or 257. Other systems use
SYS_NMLN or _SYS_NMLN or UTSLEN or _UTSNAME_LENGTH. Clearly, it is a
bad idea to use any of these constants; just use sizeof(...). Often
257 is chosen in order to have room for an internet hostname.
Part of the utsname information is also accessible via
/proc/sys/kernel/{ostype, hostname, osrelease, version, domainname}.
Clibrary/kerneldifferences
Over time, increases in the size of the utsname structure have led to
three successive versions of uname(): sys_olduname() (slot
__NR_oldolduname), sys_uname() (slot __NR_olduname), and sys_newuname()
(slot __NR_uname). The first one used length 9 for all fields; the
second used 65; the third also uses 65 but adds the domainname field.
The glibc uname() wrapper function hides these details from
applications, invoking the most recent version of the system call
provided by the kernel.

SEEALSO

COLOPHON

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